Image display device



May 17, 1960 G. A. BURDICK 2,937,297

IMAGE DISPLAY DEVICE 7 Filed Aug. 5, 1957 4 Sheets-Sheet 1 5m INVENTOR GLEN A. BURIMCK ATTORNEY y 17, 1960 G. A. BURDICK 2,937,297

IMAGE DISPLAY DEVICE Filed Aug. 5, 1957 4 Sheets-Sheet 2 PIC-3.3. 'M

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FIGJ-Lq INVENTOR eLEvg 'A. BURDlCK Mam ATTORNEY G. A. BURDICK IMAGE DISPLAY DEVICE May 17, 1960 4 Sheets-Sheet 3 Filed Aug.' 5, 1957 INVENTOR GLEN A. BURENCK ATTORNEY May 17, 1960 G. A. BURDICK 2,937,297

IMAGE DISPLAY DEVICE I Filed Aug. 5, 1957 4 Sheets-Sheet 4 LIGHT AXIS TUBE A365 RADIAL INVENTOR T G L GLEN A. BURENCK ATTORNEY United States Patent IMAGE DISPLAY DEVICE Glen A. Bur-dick, Waterloo, N.Y., assign'or, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Application August 5, 1957, Serial No. 676,253 2 Claims. (Cl. 31'3-85) This invention relates to image display devices and more particularly to cathode ray tubes of the type adapted to be employed in color television apparatus.

One of the chief problems encountered in the production of screens for image display color tubes such as those used. in television apparatus involves matching" of the light optics employed in the screen forming process with the electron optics existent in the finished tube. Unless the discrete image display elements on the screen arepositioned so that the scanning electron beam or beams will correctly register therewith, an impure or otherwise unacceptable color image will result. Many factors such as tube geometry, dynamic convergence, earths magnetic field, etc. effect registration in a manner well understood in the art. This invention is concerned in part, with that portion of the registration problem created by dynamic convergence of the electron beams employed in the tube.

It is the present practice in television art to use a continuously varying beamconvergence field in conjunction with a multiple beam color tube so that the beams can be moved relative to each other in the deflection region in :accordance with the deflection angle and direction of the beam or beams at a given instant. The mask or grid, utilized in the tube generally has a spacing from the screen such that the electron beams will cross one another at the :mask and impinge upon the screen without overlap. This mask is constructed so that the spacing from the center -of the mask to the sceren is less thanthespacing between these structures along their edges. However, with such a construction, the beam impinging spots for any given pattern are separated by a greater distance over certain areas of the screen than over other areas. In order to obtain a reasonable semblance of color purity in the .tube, the discrete'image display elements or areas are so positioned that at least a small portion of each display area will cover the associated electron beam impinging spot on the screen. The image display so produced is not uniform ;in appearance nor does it give good color uniformity. Due to the critical design, manufacturing tolerances are extremely rigid and the tube operational set-up requires :a variety of controls and is very costly and time consum- Accordingly, an object of this invention is to reduce the aforementioned disadvantages and-to provide an optimum display area with good electron beam registration, improved color uniformity, and a uniform appearing screen for an image display device.

A further object is to reduce the necessity for critical control of manufacturing tolerances. in the fabrication of image displays and to increase the operational set-up efli- -ciency. for such devices.

Another object is. toifabricate :screens and tubes.

The foregoing objects are achieved in one; aspect of the improved image display invention by theprovisionof an image display ,tubein which the'electron beam impinging spot pattern associated wi'th a'given imagev displaypa'ttern is such that the average 2,937,297 Pgtented May 17, 1960 2 distance between the center of a given beam impinging spot and the, center of the associated spot pattern has: a prescribed relationship relative to the distance between the center of the associated spot pattern and adjoining spot patterns. An exposure device and manufacturing process are provided to produce a screen having a plural.- ity of discrete display areas, the location of each discrete area being positioned in a prescribed relationship to the impinging beam positions for a given deflection angle.v

For a better understanding of the invention, reference is made to the following description, taken in conjunction with the accompanying drawings in which:

Fig. 1 is a plan view of a typical cathode ray tube adapted for the reproduction of color images;

Fig. 2 illustrates the manner in which the electron beams are dynamically converged in the tube;

'Fig. 3 shows a portion of an image display structure illustrating one embodiment of the invention;

Fig. 4 illustrates the spatial relationship between beam impinging spot patterns formed in accordance with one aspect of the invention.

Fig. 5 shows a portion of a cathode ray tube screen;

Fig. 6 illustrates the optical system employed in the screen forming process; I

Fig. 7 is an enlarged view of a portion of the discrete image display configurations showing the beam impinging spots located thereon; and

Fig. 8 illustrates the relationship between the image display areas and the electron beam impinging positions.

Referring to the drawings, Fig. lshows a typical plural beam shadow mask type cathode ray tube. Disposed within envelope 11 are three electron emitters 12 positionedapproximately 120 degrees apart to provide three electron beams 13 which may be deflected by coils 15 over the raster area and converged at mask 17 to impinge upon screen 19. The screen comprises a large number of triads, each triad consisting of discrete areas or elements of red, green and blue color fluorescing materials which are positioned at the intercepting points of the appropriate one of the electron beams 13 employed in the tube. Although a tri-gun shadow mask tube is shown in Fig. 1, it will be apparent that the invention described herein is also applicable to other plural beam types of ice . image reproduction devices.

' Two of the three beams used in a shadow mask cathode ray tube are shown in Fig. 2 to illustrate the dynamic convergence effects. The static convergence beam paths pass through points a and b in the deflection region and proceed toward mask 17 and screen 19 at an angle to the tube axis to converge at point g. -Wh en the beams 13 are deflected to some angle alpha (a) without the aid of dynamic convergence fields supplied by coils 21, the beams appear to originate from points a and b and intersect at point c. This situation is highly unsatisfactory. in practice, the coils 21 provide magnetic fields which move the beams 13 radially outward in the deflection region to cause beams 13 to appear to come from points e and f'to provide the desired convergence at point g within an aperture in mask 17. The points e and f designate positions which are approximately on the locus of motion of the apparent center of deflection for each beam 13.

It has been thepractice to use a mask 17 which has a spacing d at the center of the mask between the mask and screen 19 which is less than the spacing d at the edge of the mask. This construction, in conjunction with dybe separated by a considerable distance at the edges of the screen, as shown, or they may be separated or pulled together at other pre-selected positions by moving the entire mask towards or away from the screen in a manher well understood in the art. In any event, a tube having this type of structure produces a beam pattern which has given areas wherein the beams are undesirably separated or pulled together. This situation causes the beams to impinge upon the fluorescent dots very close to their borders at those locations on the screen where the beams are adversely affected to the greatest extent.

In order to improve the beam landing position pattern uniformity over the screen and the spacing between the beam impinging positions in a given triad, it has been found that the mask curvature should be such that the spacing s Fig. 3, along the tube axis or central portion, should-be greater than the spacing s at the edges or peripheral portions of the grid 17. This grid or mask structure takes into account the non-linearity of the fields provided by yoke coils 21, the amount of beam displacement needed in the tube for dynamic convergence, and the geometric configurations and spatial relationships of the gun electrodes 12, screen 19, etc. Since the grid or mask 17 and screen 19 are generally curvilinear in form, this spacing may be suchthat the grid to screen distance measured along the electron beam path varies inversely to the distance between the apparent source of the electron beams, e.g. points e and f, and the tube axis. To satisfy this condition, the structural relationship between the grid and screen should be such that their surfaces will intersect if projected.

A grid to screen spacing of the type shown in Fig. 3 will provide a unique pattern of beam spots over the entire screen. To illustrate this pattern, Fig. 4 shows two adjoining average triads spaced from one another in a tangential direction. The individual average beam positions in an average triad at a given deflection angle relative to the center of the triad, and the relationship between adjoining average triads may be expressed in terms of distances measured from the triad centers and O. This beam spot pattern is such that for any given triad deflection angle, the average distance from a given beam spot to the center of its associated beam spot triad is approximately one-third the tangential distance between the center of the associated triad and the center of an adjoining triad. In Fig. 4, the letters R, B and G have been used to designate the average center of two groups of impinging spots provided by the red, green and blue chroma modulated beams representing all locations on the screen defined by one deflection angle. For instance, at a 33 degree deflection angle for triad T, the distance B-O is approximately equal to one-third the tangential distance OO. This relationship is also true for the R-O and 6-0 distances in triad T in addition to the '-O', O' and G'-O' vectors in triad T.

The tangential distance between beam spot triads is used to define the relative triad positions since it is a less constant dimension over the screen than the radial dimension, and since it may be expressed in terms of a simple relationship. Figs. 1, 2 and 3 illustrate the manner in which the electron beams are converged at an aperture in mask 17 to cross one another and impinge upon screen 19 to form a triad of beam spots. The relative positions of adjoining triads are therefor dependent, in part, upon the relative positions of the apertures in mask 17. It is well known that the mask is stretched non-uniformly in a tangential direction during fabrication, with the distance between adjoining mask apertures decreasing progressively toward the mask periphery. Consequently, the beam spot triad distances also tend to decrease in this direction. However, mask stretch does not have an appreciable non-uniform effect upon the radial dimensions between mask apertures or spot triads, and, since the tangential distance is usually equal to or less than the radial dimension, it is used as a basis for the 4 beam spot and phosphor clot patterns. The phosphor dot triad pattern should fit into the smallest beam triad pattern so that there will not be an overlap of phosphor dots on the screen.

Fig. 5 illustrates the derivation of the average beam spot centers R, B, G, R, B, and G shown in Fig. 4. Three locations on screen 19 are indicated at 3 oclock, 7 oclock and 11 oclock for a deflection angle of 33 degrees. The sum of n numbers of B-O distances, i.e. +B3O3+ +B11O11 by n is approximately equal to one-third the tangential distance between the centers of adjoining triads e.g. dimension 0 -0 This relationship exists for all R, B and G beam spots located on each deflection radius over the entire screen to provide an improved beam spot pattern.

It has been found that for a 22 inch 70 degree deflection shadow mask color tube, a spacing s equal to .530 inch varying to an edge spacing of s of .491 inch provides the pattern illustrated in Fig. 5. Such a spacing may be achieved by forming the mask 17 with a radius of curvature substantially equal to the 26 inch radius used 'for the screen surface. Generally, the center of'the mask radius is positioned farther from the screen than the center of the screen radius so that even if the mask and screen have the same or a slightly smaller or larger radius, the peripheral portions of the mask will be closer to the screen than the central portions.

An optical exposure device such as that shown in Fig. 6 is used to produce an image display screen wherein the discrete fluorescent dots or areas have maximum coverage without overlap, i.e. minimum space between areas, while also providing a maximum border of fluorescent material around each beam impinging position or spot when the spot pattern is of the type shown in Fig. 5. This optical exposure device is used in the screen forming process which includes the application of a photo-printing technique. In this process, a light hardenable photosensitive material such as polyvinyl alcohol sensitized with ammonium dichromate and an appropriate fluorescent material such as the red phosphor, zinc phosphate, are deposited on the glass panel 25. Discrete areas of this coating are then exposed to light rays radiated from a point source light transmitter 27 through the lens 29 and through apertures in a negative or grid .17. The areas 23 of the sensitized coating which are exposed to light become hardened and adhere tothe glass envelope while the unexposed portions are removed by a developing fluid such as deionized water. The above process is then repeated using the blue and green phosphors, with proper off-setting of the transmitter and lens with each exposure operation to provide the complete image display screen. Zinc ortho-silicate is one example of an acceptable green phosphor material while zinc sulfide is at present considered to be a satisfactory blue phosphor.

Fig. 6 shows an optical system associated with one beam position of a multiple beam tube which is capable of positioning the discrete screen elements 23 at the location where the beams 13 will land by substantially superimposing in space the locus of motion of apparent light ray origin upon the locus of motion of apparent center of deflection of the electron beam. This relationship. is accomplished by off-setting light source 27 from the tube axis a distance p and oil-setting lens 29 a distance r and an angle beta (,8) from the axis of the transmitter. With this arrangement, the locus 32 of apparent light ray origin utilized in the screen forming process is located in space at substantially the same positionrrelative to the screen and mask as is the locus 33 of the electron beam apparent center of deflection in the operating tube. Although the light rays 26 originated from the tip of transmitter 27, they appear to come from a point on locus 33, when viewed from the screen, since they are refracted by the.plano-concave symmetrical lens 29. The amount of ofi-set and tilt of lens29 are inter-related in such a manner that an increase in offset will allow a reduction in tilt and vice-versa to achieve similar results. In addition, although a symmetrical plane-concave lens is shown, other types of lens elements could be employed in conjunction with the correct positioning of transmitter 27 and the lens 29 relative to one another and to the mask '17 and the axis of the tube to achieve the desired results. For instance, an asymmetrical and/or an aspherical lens could be used in this system with little or no tilt, if desired. It has been found that for a 22 inch shadow mask tube of the type described above, the application of a 90 millimeter diameter planoconcave lens 29 with a center thickness of .45 centimeter and a radius of curvature equal to 23.55 centimeters spaced from transmitter 27 a distance of 1.875 inches, oflset a distance r of .265 inch and tilted an angle beta (5) of 3 degrees will produce the improved phosphor dot pattern for this tube.

Referring to Fig. 7, it can be seen that the discrete image display phosphor areas or dots 23 are so positioned by the optical system shown in Fig. 6, when it has the ideal combination of tilt and ofiset, that the discrete areas are substantially tangent in a tangential direction to provide maximum coverage .of the panel 25 in addition to substantially increasing the uniformity of brightness and quality of the reproduced image while providing color pattern uniformity with a minimum amount of color impurity. The relationship between the beam impinging spots or positions 13 and the discrete phosphor dots 23 on the screen is clearly shown in Figs. 7 and 8. For any given deflection angle, i.e. for those positions on the screen located at a given radius from the axis of the screen, the centers x of the areas 23 are positioned substantially coincident with the location of the average centers y of the impinging beam spots 13. The beam positions shown by solid lines in Fig. 8 indicate one location on the screen, e.g. a 36 degree deflection angle at 3 oclock. Disposed exactly opposite (in dotted lines) to the positions shown by the solid lines would be the location of the beam spots 13 at a 36 degree deflection angle and at 6 oclock. Therefore, it can be seen that the centers x of discrete phosphor areas 2.3 are substantially coincident with the average centers y of the spots 13 at all locations on a given screen radius or for a given deflection angle. Such an arrangement provides improved registration over the entire screen and minimizes the possibility of color impurity in the reproduced image.

Referring particularly to Fig. 7, the pattern of fluorescent dots 23 is shown to consist of red, green and blue fluorescing dot triads which are substantially contiguous in a tangential direction and are separated from one another in the radial direction for reasons explained more fully in conjunction with Figs. 4 and 5. That is, if a line is drawn from the center of the screen radially outward, the successive triads which the line intercepts will be separated from one another by increasing amount with increasing deflection angle whereas the adjacent triads lying along a line tangent to the radial line will be substantially contiguous to one another. This type of phosphor pattern achieves maximum coverage of face plate 25 without overlap.

It is apparent from the foregoing description that a mask configuration has been illustrated in Fig. 3 to provide a more symmetrical and uniform beam impinging spot pattern as shown in Figs. 4 and 5. In addition, a process and exposure device such as that shown in Fig. 6 is adapted to form a phosphor dot pattern (Figs. 7 and 8) which registers with the beam spot pattern to provide a highly satisfactory image display.

Although several embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. A cathode ray tube comprising an image display screen, a grid structure having a plurality of openings arranged radially and tangentially relative to one another, and a plurality of deflected electron beams directed to approach the grid from spaced positions and be dynamically converged at the grid openings to pass therethrough and impinge upon said screen in the form of a pattern of spaced beam spots for each grid opening, said grid structure being formed and positioned relative to the screen to provide the beam spot patterns wherein the average distance between the spots and the centers of their associated patterns at a given deflection angle is substantially equal to onethird the tangential distance between the centers of said associated patterns and the centers of the next adjacent patterns located at said given deflection angle.

2. A cathode ray tube comprising an image display screen, a grid structure having a plurality of openings arranged radially and tangentially relative to one another, and three deflected electron beams directed to approach the grid from spaced positions and be dynamically converged at the grid openings to pass therethrough and impinge upon said screen in the form of a triad pattern of spaced beam spots for each grid opening, said grid structure being formed and positioned relative to the screen to provide the beam spot triad patterns wherein the average distance between the spots and the centers of their associated triad patterns at a given deflection angle is substantially equal to one-third the tangential distance between the centers of said associated triad patterns and the centers of the next adjacent triad patterns located at said given deflection angle.

References Cited in the file of this patent UNITED STATES PATENTS 2,416,056 Kallman Feb. 18, 1947 2,733,366 Grimm Jan. 31, 1956 2,745,978 Van Ormer May 15, 1956 2,755,402 Morrell July 17, 1956 2,795,720 Epstein June 11, 1957 2,801,355 Nunan July 30, 1957 2,817,276 Epstein Dec. 24, 1957 OTHER REFERENCES RCA Publication, "Recent Improvements in the 21AXP22 Color Kinescope, by R. B. Janes, L. B. Headrick and J. Evans, printed June 1956.

Notice of Adverse Decision i In Interference N 0. 91,276 involving Patent N 0. 2,937,297, mag-e display device, final judgment adverse to th ec. 27, 1962, as to claims 1 and 2.

[Ofiicz'al Gazette April 30, 1963.]

n Interference G. A. Burdick, e patentee Was rendered 

